Browsing by Author "Bai, Jingwen"

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    Distributed Full-duplex via Wireless Side Channels: Bounds and Protocols
    (2013-09-16) Bai, Jingwen; Sabharwal, Ashutosh; Aazhang, Behnaam; Knightly, Edward W.
    In this thesis, we study a three-node full-duplex network, where the infrastructure node has simultaneous up- and downlink communication in the same frequency band with two half-duplex nodes. In addition to self-interference at the full-duplex infrastructure node, the three-node network has to contend with the inter-node interference between the two half-duplex nodes. The two forms of interferences differ in one important aspect that the self-interference is known at the interfered receiver. Therefore, we propose to leverage a wireless side-channel to manage the inter-node interference. We characterize the impact of inter-node interference on the network achievable rate region with and without a side-channel between the nodes. We present four distributed full-duplex inter-node interference cancellation schemes, which leverage the device-to-device wireless side-channel for improved interference cancellation. Of the four, bin-and-cancel is asymptotically optimal in high signal-to-noise ratio limit which uses Han-Kobayashi common-private message splitting and achieves within 1 bits/s/Hz of the capacity region for all values of channel parameters. The other three schemes are simpler compared to bin-and-cancel but achieve the near-optimal performance only in certain regimes of channel values. Asymptotic multiplexing gains of all proposed schemes are derived to show analytically that leveraging the side channel can be highly beneficial in increasing the multiplexing gain of the system exactly in those regimes where inter-node interference has the highest impact.
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    Vector bin-and-cancel for MIMO distributed full-duplex
    (Springer International Publishing, 2017) Bai, Jingwen; Sabharwal, Ashutosh
    Abstract In a multi-input multi-output (MIMO) full-duplex network, where an in-band full-duplex infrastructure node communicates with two half-duplex mobiles supporting simultaneous up- and downlink flows, the inter-mobile interference between the up- and downlink mobiles limits the system performance. We study the impact of leveraging an out-of-band side channel between mobiles in such network under different channel models. For time-invariant channels, we aim to characterize the generalized degrees-of-freedom (GDoF) of the side-channel-assisted MIMO full-duplex network. For slow-fading channels, we focus on the diversity-multiplexing tradeoff (DMT) of the system with various assumptions as to the availability of channel state information at the transmitter (CSIT). The key to the optimal performance is a vector bin-and-cancel strategy leveraging Han-Kobayashi message splitting, which is shown to achieve the system capacity region to within a constant bit. We quantify how the side channel improve the GDoF and DMT compared to a system without the extra orthogonal spectrum. The insights gained from our analysis reveal (i) the tradeoff between spatial resources from multiple antennas at different nodes and spectral resources of the side channel and (ii) the interplay between the channel uncertainty at the transmitter and use of the side channel.
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    Wireless Side-Channels in MIMO Full-Duplex Systems
    (2016-04-25) Bai, Jingwen; Sabharwal, Ashutosh
    In this thesis, we propose a new approach for enhanced interference management via wireless side-channels in advanced wireless systems such as MIMO full-duplex systems. The rise of multiple radio interfaces, such as WiFi (operating in unlicensed ISM bands) and cellular (operating in licensed bands), with near-default inclusion in smartphones, allows for a new use of the ISM bands to manage interference in cellular bands, by creating wireless “side-channels” between mobile users. In a multi-user MIMO full-duplex system, an in-band full-duplex base station (BS) with multiple antennas communicates with multiple up- and downlink users in the same time-frequency slot. We characterize the impact of side- channels in managing interference from uplink users to downlink users in such MIMO full-duplex system. First, we experimentally quantify the likelihood of establishing ISM side-channels between smartphones in WiFi-free areas such as highways. Next, we study a side-channel assisted two-user MIMO full-duplex sys- tem and characterize its generalized degrees-of-freedom and diversity- multiplexing tradeoff. For such a system, we show that the optimal perfor- mance is achieved by our proposed vector bin-and-cancel strategy which leverages Han-Kobayashi message splitting. Then, we study a side-channel assisted multi-user MIMO full-duplex system from a cross-layer protocol design perspective. Our protocol design integrates automatic repeat request (ARQ) at the medium access control (MAC) layer with enhanced interference management via side-channels at the physical layer (PHY). Our proposed joint PHY-MAC protocols exploit the ARQ information offered by the MAC layer to reduce the data retransmission time and improve system goodput. Finally, we study a multi-cell multi-user MIMO full-duplex system, where new forms of intra- and inter-cell interference appear due to the full-duplex operation. We characterize the up- and downlink ergodic achievable rates for the case of linear precoders and receivers. The rate analysis includes practical constraints such as imperfect full-duplex radio chains, channel estimation error, training overhead and pilot contamination. We show that with large antenna arrays at base-stations, the gains from full-duplex are available at the network level despite the increased interference in the full-duplex networks. Moreover, full-duplex networks can use fewer antennas to achieve spectral efficiency gain over the half-duplex counterparts. We also demonstrate that under realistic multi-cell MIMO full-duplex network scenarios, side-channels are effective in significantly improving the spectral efficiency of cell-edge users.